66 TERRESTRIAL MAGNETISM. 



Journal de Physique, T. Ixix. 1804, p. 433, with the first 

 sketch, of a map of the intensity ; Kosmos, Bd. i. S. 432, 

 Anm. 29 ; Engl. ed. p. 416, Note 159). Subsequent ob- 

 servations have shown that the minimum of intensity is not 

 situated on the magnetic equator ; and that the increase of 

 force in either hemisphere does not extend to the magnetic 

 pole. 



1805 1806. Gay-Lussac and Humboldt's observations 

 on the magnetic force in the South of France, Italy, Switzer- 

 land, and Germany (Memoires de la Societe d'Arcueil, T. i. 

 p. l-r-22.) Compare therewith the observations of 

 Quetelet, 1830 and 1839, published in the Mem. de 

 F Academic de Bruxelles, T. xiv., with a map of the hori- 

 zontal magnetic force between Paris and Naples ; Forbes's 

 observations in Germany, Flanders, and Italy, in 1832 and 

 1837 (Transactions of the Eoyal Society of Edinburgh, 

 Yol. xv. p. 27) ; the very exact observations of Rudberg in 

 France, Germany, and Sweden, 1832; and the observations 

 of Bache (Director of the Coast-Survey of the United 

 States), of inclination and force, at 21 stations in 1837 

 and 1840. 



1806 1807. A long series of observations at Berlin 

 on the horary variations of the declination, and on the 

 recurrence of " magnetic storms/' (perturbations or dis- 

 turbances), by Humboldt and Oltmanns, made chiefly at 

 the solstices and equinoxes for five or six, or sometimes 

 even nine, successive days and nights, with a Prony's 

 magnetic telescope reading to 7 or 8 seconds of arc. 



1812. Statement by Morichini at Rome that unmagnetised 

 steel needles became magnetic by contact with light (with 

 the violet ray). On the long controversy occasioned by this 



